The molecular genetics of the agouti locus will be investigated, using as a starting point a closely linked molecular probe. The agouti coat color locus of the mouse controls the relative amount and distribution of pigment in the coat hairs. Mutations at this locus have pleiotropic effects on a wide range of processes including tumor incidence, obesity and embryogenesis, as well as pigment deposition. The top dominant lethal yellow (A/y) allele at this locus is closely linked to an endogenous provirus (emv-15) in three inbred strains. This provirus has apparently altered a flanking host gene by promoter insertion and results in the production of hybrid viral-host transcripts. Using unique mouse DNA probes from regions flanking Emv-15 the possible role of this provirus in the prenatal lethality of Ay homozygotes will be investigated. The gene that flanks Emv-15 will be further investigated to determine whether it is within the agouti locus, and the exact effect that the Emv-15 integration has had upon this gene will also be investigated. The breakpoints of two reciprocal chromosomal translocations that affect agouti locus function, and of several potential deletions within this region, will be mapped relative to the Emv-15 integration by pulsed field gel electrophoresis. Molecular clones spanning these regions will then be isolated by a process of "chromosome walking". The location of the agouti locus within these clones will then be determined by assaying selected subclones for transcriptional activity within skin at defined stages of hair growth and pigment deposition. The activity of this gene(s) will then be further sublocalized to specific regions within hair bulbs by in situ hybridization to skin cross sections.